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+Locking
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+=======
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+
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+Very simple plugin which adds the aquire_lock method to active record base. This is mysql only.
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+
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+As long as a lock of a certain name is acquired no other connection on the server is able to aquire the same lock. 
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+This is very useful for background tasks such as billing or search server re-indexing which would cause errors when they 
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+would be ran from multiple machines at the same time but you still want to run them from multiple machines at the same time 
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+for redundancy reasons. 
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+
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+Example
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+=======
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+                                                                                                                              
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+Invoice.aquire_lock("Shopify billing") do
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+
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+  Invoice.find_all_due.each { |invoice| invoice.collect_payment! } 
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+  
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+end
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+
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+
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+Usecase
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+=======
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+                    
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+# save to run on several machines at the same time: 
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+ 
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+ ./script/runner 'Invoice.aquire_lock("Shopify billing") {  Invoice.find_all_due.each { |invoice| invoice.collect_payment! } }'
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\ No newline at end of file

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+require 'locking'
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+
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+ActiveRecord::Base.send(:include, Locking)
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\ No newline at end of file

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+module Locking
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+  class LockError < ActiveRecord::ActiveRecordError
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+  end  
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+  
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+  class LockTimeout < LockError      
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+  end    
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+  
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+  def self.included(base)
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+    base.send(:extend, ClassMethods)
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+  end
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+    
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+  module ClassMethods
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+    
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+    # Aquires an application level lock in the mysql server. 
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+    def aquire_lock(lock_name = table_name, wait_timeout = 0)
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+      case c = connection.select_value("SELECT GET_LOCK(#{quote_value(lock_name)}, #{quote_value(wait_timeout)})")
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+      when '1' 
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+        yield if block_given?
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+      when '0' 
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+        false
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+      when 'NULL'
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+        raise LockError, "Error in locking mechanism"
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+      else
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+        raise LockError, "Unknown response from database: #{c.inspect}"
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+      end
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+      
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+    ensure
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+      connection.select_one("SELECT RELEASE_LOCK(#{quote_value(lock_name)})")
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+    end
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+    
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+    # Aquires an application level lock in the mysql server. Throws Locking::LockTimeout if the 
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+    # lock cannot be aquired.
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+    def aquire_lock!(lock_name = table_name, wait_timeout = 0, &block)
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+      aquire_lock(lock_name, table_name, &block) or raise LockTimeout, 'Timeout waiting for lock'
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+    end
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+    
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+  end
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+  
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+end